.edgeOrder(network.edgeOrder());
  }

  /**
   * Returns an {@link ImmutableNetwork.Builder} with the properties of this {@link NetworkBuilder}.
   *
   * <p>The returned builder can be used for populating an {@link ImmutableNetwork}.
   *
   * @since 28.0
   */
  public <N1 extends N, E1 extends E> ImmutableNetwork.Builder<N1, E1> immutable() {
    NetworkBuilder<N1, E1> castBuilder = cast();

      NetworkBuilder.directed().allowsSelfLoops(true).expectedNodeCount(16);

  private static final ImmutableNetwork<String, String> IMMUTABLE_NETWORK_A =
      NetworkBuilder.directed().<String, String>immutable().addNode("A").build();
  private static final ImmutableNetwork<String, String> IMMUTABLE_NETWORK_B =
      NetworkBuilder.directed().<String, String>immutable().addNode("B").build();

      NetworkBuilder.directed().allowsSelfLoops(true).expectedNodeCount(16);

  private static final ImmutableNetwork<String, String> IMMUTABLE_NETWORK_A =
      NetworkBuilder.directed().<String, String>immutable().addNode("A").build();
  private static final ImmutableNetwork<String, String> IMMUTABLE_NETWORK_B =
      NetworkBuilder.directed().<String, String>immutable().addNode("B").build();

 * ImmutableNetwork}.
 *
 * <p>You can create an immutable copy of an existing {@code Network} using {@link
 * ImmutableNetwork#copyOf(Network)}:
 *
 * <pre>{@code
 * ImmutableNetwork<Integer, MyEdge> immutableGraph = ImmutableNetwork.copyOf(network);
 * }</pre>
 *
 * <p>Instances of {@link ImmutableNetwork} do not implement {@link MutableNetwork} (obviously!) and

 * ImmutableNetwork}.
 *
 * <p>You can create an immutable copy of an existing {@code Network} using {@link
 * ImmutableNetwork#copyOf(Network)}:
 *
 * <pre>{@code
 * ImmutableNetwork<Integer, MyEdge> immutableGraph = ImmutableNetwork.copyOf(network);
 * }</pre>
 *
 * <p>Instances of {@link ImmutableNetwork} do not implement {@link MutableNetwork} (obviously!) and

    validateNetwork(network);
  }

  static <N, E> void validateNetwork(Network<N, E> network) {
    assertStronglyEquivalent(network, Graphs.copyOf(network));
    assertStronglyEquivalent(network, ImmutableNetwork.copyOf(network));

    String networkString = network.toString();
    assertThat(networkString).contains("isDirected: " + network.isDirected());